In comparing patients with mild (grade 0-3) CRS to those with severe (grade 4-5) CRS in patients treated with a 4-1BB CD19-directed CAR-T product, Teachey et al. found IFNγ, IL-6, IL-8, sIL-2R, sgp130, sIL-6R, MCP1, MIP1α, MIP1β, and GM-CSF to be significantly associated with the more severe grades [20]. The gene discussed is CSF2; the disease is congenital rubella syndrome.